The present invention relates to a plant substrate containing 20 to 100% of a granulate of foamed clays or lightly fired ceramic materials, as well as the uses thereof.
Plant metabolism is characterized essentially by the following processes dissimilation (respiration), assimilation (photosynthesis), nutrient exchange, water economy and transpiration. For optimum growth, the plant requires, in addition to atmospheric influences (climate, light, etc.), a fixed support and a continuous and sufficient supply of nutrients and water from its substrate. Composition and structure of the substrate are therefore essential growth factors.
Plant organisms require water not only as a starting compound for photosynthesis but also as an important reaction partner in metabolic processes. Accordingly, the water content of the organisms is high: the percentage by weight of water may amount to up to 90% or more of the living substance of higher plants. A continuous flow of water takes place in the plants, the water being driven into the upper parts of the plants by permanent evaporation (transpiration). This loss of water must be compensated for by a corresponding absorption of water. Plant organisms can basically employ their entire surface for the absorption of water. Plants which have a root, however, supply themselves from the substrate.
The absorption of nutrients is, to a great part, bound to water, since the mineral substances and, in part, also the organic substances are absorbed in aqueous solution. In addition to carbon, oxygen and hydrogen, which are incorporated in organic molecules upon photosynthesis starting from CO.sub.2 and H.sub.2 O, plants require further elements for their metabolism, namely nitrogen, sulfur and phosphorus as non-metals, as well as the metals potassium, calcium and magnesium. Furthermore, for their normal development, most plants also require trace elements, namely iron, manganese, zinc, copper, boron, molybdenum, cobalt as well as chlorine and silicon, and in some cases also sodium and selenium. Almost all of said elements are considered essential; with an insufficient supply, typical deficiency phenomena occur. For many plants, the presence of all essential elements in the soil is not sufficient. Rather, their amounts must also be in a favorable ratio to each other. Furthermore, the manner in which the nutrients are bound to the substrate, and thus their availability, constitutes a critical variable supplying the nutrients to the plant.
The well-being of the plant is therefore dependent to a great extent on physical and chemical properties of the substrate. Important physical parameters include the volume of the soil, the exchange capacity of the substrate, which is dependent on its mineralogical composition, its particle size and structure, as well as the stability of the substrate structure, which is affected by various factors. The contents of organic substances such as growth, humin, inhibiting and resistance substances, etc., and of the aforementioned essential elements from inorganic substances represent the decisive chemical parameters of the substrate.
Formerly, numerous different mixtures of earth were used as plant substrates in order to satisfy the different requirements of different plants. During the last few decades, use has been made in actual practice of various standard earths and peat substrates whose water and nutrient content can be easily controlled. In addition to this, there has been increased use recently, particularly in care of house plants, of hydroponics in which the nutrients must be fed in plant-available form by watering solutions to the substrate. The substrate generally consists of expanded clay granulate. In this case, the substrate is produced by firing suitable clays at very high temperatures, and the material is expanded, i.e. irregular blisters and pores are formed, by an inner development of gas.